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In contrast, the term brightness in astronomy is generally used to refer to an object's apparent brightness: that is, how bright an object appears to an observer. Apparent brightness depends on both the luminosity of the object and the distance between the object and observer, and also on any absorption of light along the path from object to ...
The strong difference in brightness between the three is real. The left image at 0° phase angle shows the brightness surge due to the opposition effect . Phase integrals for various values of G Relationship between the slope parameter G {\displaystyle G} and the opposition surge.
Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. [1] In other words, brightness is the perception elicited by the luminance of a visual target.
The difference between these concepts can be seen by comparing two stars. Betelgeuse (apparent magnitude 0.5, absolute magnitude −5.8) appears slightly dimmer in the sky than Alpha Centauri A (apparent magnitude 0.0, absolute magnitude 4.4) even though it emits thousands of times more light, because Betelgeuse is much farther away.
A difference of 1.0 in magnitude corresponds to the brightness ratio of , or about 2.512. For example, a magnitude 2.0 star is 2.512 times as bright as a magnitude 3.0 star, 6.31 times as magnitude 4.0, and 100 times magnitude 7.0.
A truly dark sky has a surface brightness of 2 × 10 −4 cd m −2 or 21.8 mag arcsec −2. [9] [clarification needed] The peak surface brightness of the central region of the Orion Nebula is about 17 Mag/arcsec 2 (about 14 milli nits) and the outer bluish glow has a peak surface brightness of 21.3 Mag/arcsec 2 (about 0.27 millinits). [10]
N bb is a fudge factor that is normally 1; it's only of concern when comparing brightness judgements based on slightly different reference whites. Here Y is the relative luminance compared to white on a scale of 0 to 1 and L A is the average luminance of the adapting visual field as a whole, measured in cd/m 2 .
Luminance is used in the video industry to characterize the brightness of displays. A typical computer display emits between 50 and 300 cd/m 2. The sun has a luminance of about 1.6 × 10 9 cd/m 2 at noon. [3] Luminance is invariant in geometric optics. [4]